Fanconi anemia (FA) is an hereditary cancer susceptibility syndrome belonging to a group of caretaker gene diseases, and is characterized by genetic instability and cellular hypersensitivity to DNA interstrand crosslinking agents such as mitomycin C (MMC). The cellular hypersensitivity of FA to DNA interstrand crosslinks (ICLs) suggests a defect in the DNA damage response. FA proteins are believed to function at the interface between cell cycle checkpoints, DNA repair and DNA replication. There are at least twelve genes involved in FA. Thus far eleven FA genes have been identified; FANCA, -B, -C, -D1, -D2, -E, -F, -G, -J, -L, and -M (Meetei et al., Nat. Genet. 36:1219-24, 2004; Levitus et al., Nat. Genet. 37:934-5, 2005; Levran et al., Nat. Genet. 37:931-3, 2005). FANCI has not yet been identified. It is believed that monoubiquitination and/or phosphorylation of FANCD2 in response to DNA damage by cross-linking agents promotes co-localization of FANCD2, FANCD1, BRCA1, and RAD51 to damage-induced nuclear foci and activation of the Fanconi anemia pathway (Taniguchi et al., Blood 100:2414-20, 2002; Hussain et al., Human Mol. Genet. 13:1241-8, 2004; Shimamura et al., Blood 100:4649-54, 2002).
Identification of BRCA2 (breast cancer associated gene 2) as FANCD1, and FANCJ as the BRCA1-associated helicase Brip1/BACH1, suggests convergence of the FA/BRCA pathway within a larger network of proteins involved in DNA repair. This convergence is further underscored by the involvement of the FA pathway in the formation of the MRE11-RAD50-NBS1 (MRN) complex on sites of DNA damage. The MRN complex is an element of the homologous recombination pathway believed to be required for processing DNA prior to homologous recombination (Nakanishi et al., Nat. Cell Biol. 4:913-920, 2002; Kobayashi et al., DNA repair (Amst.), 3:855-861, 2004). In the absence of FA pathway activation the MRN complex fails to associate with the sites of DNA damage (Penichierri et al., Hum Mol. Genet., 11:2531-2556, 2002). It has been hypothesized that FA proteins are likely to function in ICL removal via homologous recombination repair, a variation of homologous recombination, or another mechanism, during S-phase.
It is believed that dysregulation of the FA pathway occurs in 10% of human cancers including ovarian cancer (Taniguchi et al., Nature Med. 9:568-574, 2003) head and neck cancer (Marsit et al., Oncogene 23:1000-1004, 2004), lung cancer (Marsit et al., Oncogene 23:1000-1004, 2004), cervical cancer (Narayan et al., Cancer Research 64:2994-2997, 2004) and pancreatic cancer (van der Heijiden et al., Am J. Pathol. 165:651-657, 2004). Determining the effects of potential therapeutics on the activity of the Fanconi anemia pathway is critical to the development of future anti-cancer agents and Fanconi anemia therapies. Thus, the needs exist for assays to determine the effects of therapeutic agents on the Fanconi anemia pathway.